This invention relates to improved monorail crane trucks or carriages and is herein illustratively described by reference to its presently preferred forms.
A number of proposals made over the years to improve the wear and stability characteristics of monorail crane carriages employed rollers tapered toward the monorail beam web and cantilevered on fixed, opposing horizontal shafts projecting in coalignment toward each other from opposite sides of a carriage frame yoke. Matching the taper of the rollers with the slope of the beam flange surface placed their full lengths in rolling contact with the track surfaces. Examples are found in U.S. Pat. Nos. 4,266,657 (Frost et al.); 3,971,601 (Sytsma); 4,178,856 (Dunville); 1,652,009 (Hoffmaster); and 667,868 (Cook). This was seen to be desirable as a means of stabilizing the carriage against rocking and slewing. For example, without such stabilization, offset of the crane's center of mass, or shifting of the center of mass back and forth laterally in relation to the vertical plane of the monorail beam web, could cause the carriage to rock back and forth on the track and to experience skips or intermittency in crane drive roller traction.
However, tapered roller construction has proved to be less than a satisfactory design concept because of the scouring and wear of tread and roller surfaces resulting from the inherent differential in surface speeds of the rollers along their lengths. Furthermore, application of heavy loads to the crane carriage deflecting the monorail beam track flanges downwardly caused a relatively abrupt transition from the desired stabilizing full-length, rolling contact of the roller surfaces with the flange surfaces to a zonal or line-contact condition wherein, at high loading, substantially the full weight was borne by the inner ends or tips, of the rollers adjacent to the sides of the central beam web. This led to aggravated lateral instability along with aggravated localized wear of rollers and track (beam flange) surfaces. In addition, the asymmetrical loading of bearings supporting the rollers on their respective shafts shortened bearing life.
The alternative of employing untapered, cylindrical rollers mounted on cantilevered roller shafts, in turn mounted at an incline matching the slopes of the monorail beam flange bearing surfaces, reduced the no-load and light-load scouring and wear effects mentioned above, but represented no solution to the remaining problems just described. U.S. Pat. No. 1,429,118 (Townsend) illustrates that alternative type of carriage design.
Longitudinally convex rounding of the roller tread surfaces as in U.S. Pat. No. 2,997,966 (Chapin et al.) and 2,611,326 (Smallpeice) was also proposed as an alternative configuration apparently in an attempt to achieve reduced scouring and wear effects as mentioned above and also wear distribution by progressive shifting of the contact pressure zones of the rollers back and forth on the beam flanges as a function of changing flange deflection with varying loads. However, the narrow lines or zones of running contact between the roller surfaces and the beam flanges still aggravated surface wear and contributed to carriage instability.
Costly hardening of beam flange surfaces to reduce track wear added unduly to the cost of an installation whether or not an I-beam or a wide flange I-beam was employed. Since wide flange I-beams, such as H-beams, are less expensive and more readily available than I-beams, attempts were made to use these. But, one again, the problem of aggravated wear with increasing load conditions, aggravated now by the greater flange width in relation to flange thickness, hence greater deflectability of the flanges under load, aggravated the wear and instability problems. Reinforcement of the lower beam flange against load deflection by bottom paltes welded to the bottom face of the beam materially reduced flange deflection under load but added materially to installation cost.
An object of the present invention is to provide an improved monorail crane carriage of relatively lwo cost and one which mitigates or overcomes the problem limitations described above.
A more specific object hereof is to provide a crane carriage roller and mount system with reduced roller and track surface wear and with improved average lateral crane stability over a wide range of load conditions. At the same time, the invention provides a system of bearings for the crane rollers functioning to carry the loads and to transfer loads from the carriage shafts to the track surfaces with favorable distribution under varying conditions of loading of the carriage.